Many different types of water cooling tower systems are known in the art. In a typical cooling tower system, water is recirculated past a heat exchange mechanism and a cooling mechanism and is collected in a basin or reservoir located at the base of the tower. As recirculating water is lost due to evaporation during the cooling process, make-up water must be added to the system. In addition, as water evaporates, the concentration of corrosive solids present in the recirculating water increases. Accordingly, in some instances, it is desirable to bleed off a portion of the recirculating water to reduce the concentration of solids present in the recirculating water. Further, chemicals are added to the recirculating water for any of a number of reasons including the prevention of corrosion. It is important that the concentration of chemicals in the recirculating water be constant and controlled in order to prevent corrosion and scaling. Prior water treatment systems are costly, complex and subject to considerable maintenances.
One such prior water treatment system is electrically controlled. In this type of system, a water meter with an electrical contact head measures the amount of make-up water that has been added to the cooling tower. After a certain amount of make-up water passes through the meter, an electric switch mounted on the meter head is activated. This electrical switch then activates an adjustable reset timer, which, in turn, operates a chemical feed pump and an electrically operated solenoid bleed valve. The chemical feed pump is independently adjusted to deliver the desired chemical quantity based on the amount of water added to the tower. The amount of water bled to waste from the recirculating water is controlled by a manual hand valve on the solenoid bleed valve and is proportional to the of amount of water circulating through the system. This system is expensive due to costly electrical meters, switches, and valves and is subject to considerable maintenance due to failure of the switches, meters, valves, diaphragms, etc.
Another prior water treatment system is a feed and bleed system which employs a conductivity probe to control the chemical concentration in the recirculating water. The conductivity probe senses a decrease in the electrical resistance of the recirculating water in the cooling tower due to an increase in the amount of dissolved solids in the recirculating water. After a specific conductivity value is sensed, a controller for the probe activates an electrical circuit, which, in turn, activates a chemical feed valve and an electrically operated solenoid bleed valve. The chemical feed valve is adjusted to control the amount of chemicals added to the recirculating water. The bleed valve, once activated, operates to bleed a portion of the recirculating water to waste until the water resistance increases to a pre-set value. At this point, the conductivity probe controller deactivates the electric circuit, which, in turn, deactivates the bleed valve and chemical feed valve.
The addition of make-up water is controlled separately from the addition of chemicals and operation of the bleed valve. When the water in the basin decreases below a set value, a valve and sensing mechanism causes make-up water be added to the system until the water level in the basin increases above a set point. This system is even more expensive than the electrically controlled system described above due to costly sensors and is also subject to considerable maintenance. In addition, because the chemical feed is controlled separately from make-up water feed, chemicals may be introduced into the recirculating water while no make-up water is being added, or alternatively, the addition of make-up water may continue while no chemicals are being added. As a result, the chemical concentration in the recirculating water is inaccurate and poorly mixed.
Thus it is a problem in the prior art to provide an accurate, well mixed, chemical dosage system for small and medium sized cooling towers. It is also a problem in the prior art to provide a controlled bleed for small and medium sized cooling towers. In addition, it is a problem in the prior art to provide an inexpensive and low maintenance way to maintain a minimal chemical dosage and save on water usage in a cooling tower system.